Orbital angular momentum in triatomic molecules

Abstract

The electronic orbital angular momentum effects in the à ¹II _u state of C₃ have been considered. A very good fit to the observed vibronic energy levels and rotational constants has been obtained using a full matrix treatment of the orbital angular momentum in conjunction with a large amplitude formalism for the bending motion. The importance of the variation of the expectation value <L_z > with bond angle is emphasized; the quality of the final fit is very much improved when this is included. Franck-Condon overlap integrals have been calculated for bands of the à ¹II _u -[Xtilde] ¹Σ _g ⁺ transition, which is the carrier of the 4050 Å group of bands prominent in cometary spectra. A comparison has been made between the vibronic energy levels of linear and quasi-linear molecules in orbitally degenerate electronic states.